This invention relates to a traffic information system which generates traffic data by using the data on the travel histories of vehicles and distributes the generated traffic data through radio communication.
There have recently been developed floating car based traffic information systems which generate traffic data by using the data on the travel histories of vehicles. When such a system generates the traffic data on the roads which a vehicle traveled and distributes the generated data by radio communication, it is possible to provide traffic data of high instant availability by increasing the process speed of the system, and thereby increasing the renewal frequency of the traffic data. The user of an in-vehicle navigation system that utilizes such traffic data through radio reception, can foresee the traffic condition such as road congestion and choose one of paths for circumventing such traffic jam.
Since this traffic information system generates such traffic data depending on the speed at which a vehicle is supposed to have actually traveled a certain path, the traffic information system must use such data on the travel history of the vehicle as to enable the path that the vehicle has traveled along to be accurately determined in order to provide the traffic data with high accuracy.
To realize this in the simplest way is to use the detailed travel history data obtained by sampling and recording the travel history of vehicle at short temporal or spatial intervals. However, such detailed travel history data entail a huge data size which leads to a heavy process load and therefore prolonged process time. Further, when such detailed travel history data are used in communications through networks, a great communication cost will be incurred. Therefore, it is not preferable to use such detailed travel history data as it is for the floating car based traffic information system which must generate traffic data of high accuracy and high instant availability.
In order to improve the instant availability of the traffic data, therefore, the requirement must be satisfied that the amount of data on the travel history of vehicle as well as the data process time of the system must be reduced. According to JP-A-2005-149465 which discloses the system that has solved the problem of data size, the technique of data compression is used to reduce the size of data on the travel history and therefore to reduce the communication cost. This system, however, incurs a new process load such as data compression and decompression so that process time will be increased.
There is known a method of using the travel history data obtained by recording the travel history of vehicle at temporal or spatial intervals longer than those at which the above mentioned detailed travel history data are obtained by recording the travel history of vehicle. With this method, since the interval of collecting data becomes longer, the size of the data on travel history is reduced so that the process load is reduced, and the process speed is increased. As a result, however, there is possibility that the accuracy with which the travel path is determined depending on the travel history data is adversely affected. Such accuracy can be improved by utilizing the driver's disposition in choosing travel paths extracted from the way he chose his travel paths in the past, as compared with the case where no such driver's psychology is considered.
Examples of the in-vehicle navigation system which offers to the driver the travel paths selected in accordance with his disposition in choosing travel paths, include the conventional arts disclosed in JP-A-2002-107169, JP-A-2005-195358 and JP-A-2006-177792. However, since those systems obtain travel history data by recording the travel history of vehicle at relatively short temporal or spatial intervals, the resulted travel history data becomes immense in size and therefore cannot be used for the floating car based traffic information system without somehow reducing the data size.